.pentagon {
  position: relative;
  width: 200px;
  height: 0;
  border-style: solid;
  border-width: 100px 40px 0;
  border-color: skyblue transparent;
  top: 70px;
}

.pentagon:after {
  position: absolute;
  width: 0;
  height: 0;
  border-bottom: 80px solid skyblue;
  border-left: 100px solid transparent;
  border-right: 100px solid transparent;
  content: '';
  top: -180px;
  left: -40px;
}
